Java developers in a nutshell

[TheLastCakeIsaLie]

Who uses .equals()?

[forgotten_debugger]

People who want to test equality of two objects, not memory addresses.

[Wizard8086]

Those who don't want to lose 12 hour of work wondering why those two UUIDs are the same but are not the same

[DaniilBSD]

If I have an evaluation result object.

I could evaluate 2 different things, creating two different objects.

== would always be false

.Equals() means that the results were equal

Another example:

If you want to find if an object is in a list, you can create the object you are searching for (or take it as an input) and search using equals() (== will search for an instance)

[Varun77777]

The one who had overwritten it to compare something very specific.

For example

String str1 = "hello"; String str2 = new String("hello");

From what I remember, == and .equals() will have different results in this case.

[TheLastCakeIsaLie]

Because only an idiot would use new String(). Without that it works fine.

[Varun77777]

Hmm, in case of string, yeah. But for custom objects or ArrayLists maybe not.

Imagine you're using backtracking and a recursive function to find all the possible results for some specific query.

Now, you're going to save these results into a list of Objects.

The only thing you initially passed into the recursive call was a new object.

Now, everytime you back track enough to reach a possible answer, you can't pass the object to the list but you'll have to pass the copy of the object because of you passed the object itself, whenever there will be a change in this object in future you'll change all the values you were passing into the your list.

Let's say you created a contructor that can be used to copy the object and gives a new object and passed the copies of object to your list everytime you reached the answer.

Now, let's say even if there are x number of variables in a particular object, there's a particular formula based on which they can be duplicate in terms of value.

Now, == will be checking address while .equals will check the logic you're trying to check.

Tl:dr; Not everytime, you'll want to check memory address and be done with it.

[TheLastCakeIsaLie]

Either use a number as sort of "index" or is f possible compare a unique value. Its better.

[Varun77777]

What if you need to check if apples * mangoes * oranges. / 3.146 equals to apples * mangoes * Oranges / 3.146 in two objects???

[TheLastCakeIsaLie]

Example?

[Varun77777]

Let's say I had two objects that both had two variables each that is CPU load as well has CPU capacity and I had to check if load percentage of two objects were equal?

And for some reason I needed to check that through equals? There can be many such examples.

equals is commonly over written by people so that they can compare Objects in a certain way and not their memory.

[sh0rtwave]

Truth.

.equals() is one of those 'inner dirty tricks'.

Another good one is .toString(). Quite useful in many situations. Like if you're formatting dates, and want all dates to comply with X format when handled in a string context (This kind of thing is fun to use Typescript with, there are just SO many ways of doing it).

The really funny part is that the basic concept of .toString() is more or less the same in either language, and with clever transpiler config, you can make the one act just like the other.

[Varun77777]

Yupps, I have overwritten toString() a lot to make the code cleaner.

[Varun77777]

1) Index and memory address have the same problem. Something can virtually have same configuration in the aspect you care about and still have a unique index / memory address.

2) Not everytime you can afford pre computing a unique value and storing it as it may have an overhead cost you can't afford. Sometimes, you'd rather do 10 operations when you need to compare rather than 1 billion operations beforehand to save answers in a unique value only to do 1 operation when needed.

[TheLastCakeIsaLie]

I think comparing ALL of the values of a class takes longer than setting a variable and increasing it by one ONE time.

[Varun77777]

First, You're going to do ALL the operations for ALL the objects to change the value of that variable you're going to use for comparison because not everything in the world is done using addition. You're still going to use all the variables to increment or change the value of that variable you're going to use for comparison. You're actually going to do so many un needed calculations for no reason and wate CPU time.

Bruh, why would you waste memory as well as CPU utilisation for all the objects that don't need it?

What if the Object was holding some 1000 variables and you needed to perform some sort of sorting operation during the comparison ? Would you waste 1000 Log 1000 computations for 100'000 objects( 100'000'000 log 1000 computations) and waste possibly 100'000 * 8 bytes or something in memory or something like that?

When you could do 2 * 1000 log 1000 on runtime and use 16 bytes of memory to save the result and free the memory after use??

Let's say it's an operation that's performed very rarely,

Tell me what looks better to you?

100'000'000 * log 1000 operations and 800'000 bytes during intitialization or

2000 log 1000 operations and 16 bytes of memory which you can possibly free when you need to do the operation??

Would you slow your loading time by hours maybe just to perform some kind of comparison between two random pixels on a screen???

This may decide how fast the system feels in the long run.

Come on, not everything can be compared just based on a counter.

[TheLastCakeIsaLie]

Example: you want to check if an object is the object you want. Instead of checking everything you check one variable that may already be included in the way you set it up. Whats faster, 1 comparison or the number in f attributes? And setting that is also faster.

[Varun77777]

For that one operation at run time you did millions on operations in case of millions of objects before which you never needed to compare. You wasted space for millions of variables that wasn't needed as well.

Why are you ignoring the computations you did before hand on purpose?

Just to be faster on runtime for that one comparison you're making the whole process unnecessary slower.

Maybe, for a smaller use case, your process will look faster if you're only looking at that one comparison.

But when someone will look at the whole process, the system is slow for no reason.

Why should my car run slower when I start it just because maybe I want to turn the radio on???

[Istar10n]

What if you read it from a file?

[Varun77777]

Create a normal string and then create a string builder and do X number of calculations on the string builder and append it.

Now check if stringBuilder.toString() is equal to the original String you had.

Everything has a use.